The relationship between observed clinical phenotypes and underlying genotypes is blended or skewed in multiple molecular diagnoses, complicating a comprehensive molecular genetic diagnosis. We report two families with dual diagnoses, using the deafness-associated gene, COL4A6, to exemplify its contribution to blended, complex clinical presentations. This is an observational study within a large, ethnically diverse rare disease cohort, focusing on families with hearing loss and suspected dual diagnoses, followed by functional and structural studies of novel variants. Families were identified through a large rare disease sequencing initiative. Exome or genome sequencing was performed, with follow-up RNA studies for a synonymous COL4A6 variant. Spatial and temporal expression analysis in zebrafish traced col4a6 expression in the otic vesicle and ear from 1 to 5 days post-fertilization. Structural modeling was used to estimate variant impact on protein structure. We identified two families affected by multiple genetic disorders. The first family presented a missense COL4A6 variant (NM_033641.4:c.1480G>A p.(Gly494Arg)), accounting for hearing loss, while a likely pathogenic HEXA variant (NM_000520.6:c.902T>G p.(Met301Arg)) explained Tay-Sachs disease features. The second family exhibited a synonymous COL4A6 variant (NM_033641.4:c.1767G>A p.(Pro589=)), leading to partial exon skipping and hearing loss, along with a pathogenic splice-site variant in DYM (NM_001353214.3:c.1125 + 1G>T p.?), causing the Dyggve-Melchior-Clausen disease phenotype. Our findings highlight the importance of recognizing dual molecular diagnoses to untangle blended phenotypes, as well as the diagnostic relevance of synonymous variants with predicted splicing effects.

Dyggve-Melchior-Clausen (DMC) disease is a rare autosomal recessive disorder primarily characterized by spondylo-epimetaphyseal dysplasia, intellectual disability, and distinctive facial features. Patients typically present with severe developmental delays and cognitive impairments, defining features of the syndrome. This case report examines a 13-year-old Moroccan child diagnosed with DMC disease, presenting classical skeletal abnormalities, including spondylo-epimetaphyseal dysplasia, as confirmed through exome sequencing. Notably, the child exhibited a mutation recurrently identified in the Moroccan population. However, the patient showed no signs of developmental delay or intellectual disability, a marked deviation from the traditionally described phenotype. This finding suggests a broader clinical variability associated with DMC disease, emphasizing the importance of individualized assessments. This atypical presentation expands the phenotypic spectrum of DMC disease, challenging its conventional diagnostic criteria. Further research is required to elucidate the factors influencing phenotypic variability in DMC and to explore potential genotype-phenotype correlations. Early identification and documentation of such atypical cases are critical for refining diagnostic and management strategies for rare disorders.

With the focus on an idiographic approach whereby the observations incorporated the various dimensions of individual functioning 'top-down' to 'bottom-up', this case report describes the successful management of a 14-year-old girl with Kearns-Sayre syndrome and Dyggve-Melchior-Clausen disease requiring a transvenous permanent pacemaker implantation for complete heart block. The patient presented to a tertiary care centre in Muscat, Oman, in 2023 seeking consultation. The current idiographic approach appears to have a heuristic value for 2 interrelated reasons. Firstly, it is unlikely that even tertiary care units can accrue such rare presentations and scrutinise them under nomothetic approach. Secondly, by employing the idiographic approach that is capable of examining each case in-depth, the aspiration for good health and well-being may come to the forefront. To the best of the authors' knowledge this is the first published idiographic report in anaesthesia care.